In recent years, environmental issues, such as global warming, and energy issues, such as depletion of fossil fuels, have been highlighted as carbon dioxide emissions caused by the use of fossil fuels increase. Therefore, the demand for clean energy is rising every year, and one solution to those issues is an SSPS scheme.
In an SSPS scheme, as shown in FIG. 8, an artificial satellite equipped with huge solar panels is launched into space above the equator, and electric power generated from sunlight is converted into microwaves by transmission modules provided in the solar panels. Then, microwaves 100 are sent from a microwave transmitting section 101 to an electric-power receiving facility (rectenna system) 102 provided on the ground, are then re-converted into electric power on the ground and are utilized.
Thus, clean energy can be stably supplied without depending on the weather and time zone, which are drawbacks of solar power generation. There are technical problems in realizing this scheme, such as bulk electric-power transmission, microwave-beam control, and reducing operating costs, and an example method for solving those problems is to use a laminated active integrated antenna (Active Integrated Antenna: AIA) for the microwave transmitting section 101. Furthermore, in order to achieve even higher efficiency in power transmission, one approach that is being considered is to provide a retrodirective function in the laminated active integrated antenna.
The retrodirective function is a function in which a pilot signal (guide signal) sent from the electric-power receiving facility (rectenna system) 102 provided on the ground is received by a power transmission antenna provided in the microwave transmitting section 101, and phase information of the received pilot signal is reflected in the transmission waves radiated from the power transmission antenna, so that the transmission waves are directed in the arrival direction of the pilot signal.
Furthermore, in the power transmission antenna used in SSPS, two-dimensionally-arrayed antenna panels each about one-meter square are connected at connection points, forming a large-area antenna. There is a case in which, when the large-area antenna is bent at the connection points, the phase planes of microwaves radiated from the antenna panels are different, and spurious waves with a high electric-power level are radiated onto points other than the target point; therefore, methods for aligning the phase planes have been proposed.
For example, PTL 1 discloses an example retrodirective function in which the distances between an antenna reference line perpendicular to the arrival direction of the pilot signal and antenna elements are calculated based on arrival-direction angles between the arrival direction of the pilot signal and the antenna panels, and phase shifts of microwaves to be radiated from the antenna elements are set and corrected according to the calculated distances.